1. Field of the Invention
This invention relates generally to a wheeled vehicle designed to turn about a vertical axis. In particular, the invention relates to powered utility riding vehicles of the type useful for aircraft servicing operations, airport passenger vehicles, lawnmowers, warehouse utility vehicles, wheelchairs, or in any vehicle where rotation-in-place steering is advantageous.
2. Description of Prior Art
Prior art vehicles are known for turning with a zero turning radius, or so called “turning on the spot.” U.S. Pat. No. 3,938,608 describes a vehicle with a single center mounted pivoting drive motor that is rotated about a vertical axis in order to change directions of the vehicle. The '608 vehicle is supported with three or more swivel wheels located at equal radial distances from the center wheel. The '608 outer profile is in the shape of a rectangle and has appendages that make close proximity maneuvering impossible next to another object such as a post or another vehicle. Furthermore, the '608 vehicle lacks tractive force because of the single drive wheel. Furthermore, a single drive wheel must be rotated in order to change the vehicle direction, and although the single drive wheel can be turned to direct the vehicle in any direction, it does not provide directional stability for the case where a force is exerted on the vehicle from an angle to the line of intended travel. For example, a force against the '608 vehicle at a 20° angle to the right or left of the line of travel would force the single '608 wheel to skid, causing loss of directional control.
The prior art concerning aircraft service vehicles has not fundamentally changed in the last fifty years. Conventional tow vehicles for aircraft, often called tractors, are typically configured with two axles, one in front, the other in the rear. The rear axle is fixed to the vehicle and provides motive force; two additional wheels are located at the front end of the vehicle, each being steerable and connected together to provide steering of the vehicle. Since there is a distance between the fixed rear drive wheels and the axis of the steerable wheels at the front end of the vehicle, a turning radius is required that far exceeds the space actually occupied by the vehicle itself. The longer the distance between front and rear axles, the larger the turning radius that is required to change directions of the vehicle. A large turning radius makes maneuvering around crowded airport ramp areas difficult and often dangerous. Operators are required to look over their shoulders in order to back up, and congestion is commonplace at airport and air service facilities. All the vehicles around an airport ramp share these common shortcomings. A need exists for a service vehicle that requires less square footage for its footprints as well as the space required for maneuvering so that operator safety and the safety of the aircraft are enhanced.
Mowing vehicles share common problems with those of aircraft service vehicles. Commercial mowers used to mow highways and large areas commonly use row-crop tractors to pull the mowers. Such tractors are designed to pull heavy loads such as plows in a straight line with few turns, but mowing requires maneuvering around obstacles such as post, rails, and curbs. Furthermore, mowing must be for ravines, ditches and on hillsides. Rolling over or tipping of such equipment is a common problem and safety hazard. A vehicle that requires no more room than it occupies in area for maneuvering and having a low center of gravity would be very advantageous for all commercial mowing applications.
3. Identification of Objects of the Invention
A primary object of this invention is to provide a service vehicle that has enhanced maneuverability.
Another object of the invention is to provide a service vehicle that can turn on the spot and be of the smallest physical size relative to the space it occupies.
Another object of the invention is to provide a service vehicle which reduces the risk of accidents which result in damage or injury to equipment or operating personnel.
Another object of the invention is to provide a service vehicle having an outer perimeter that defines an outer imaginary cylinder that encloses any equipment or appendages mounted on the vehicle thereby enhancing its capability to maneuver the vehicle without hanging up on objects external to the vehicle.
Another object of the invention is to provide a service vehicle with structures mounted thereon for materials handling or people transport.
Another object of the invention is to provide a service vehicle that can be used for towing, pushing or handling aircraft equipment.
Another object of the invention is to provide a mowing machine that can turn on the spot and maneuver easily about obstructions.
Another object of the invention is to provide a people-moving cart for use at an airport, where the cart can turn around on the spot and be of the smallest physical size relative to the space it occupies.